net: drop bad gso csum_start and offset in virtio_net_hdr

PATCH In review [email protected] 3 participants 3 messages Sep 3, 2024 – Sep 5, 2024

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Networking Stable branch virtio core TCP +1 more subsystems

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2024-09-03 08:43 UTC #0 lore raw

PATCH 1/1 net: drop bad gso csum_start and offset in virtio_net_hdr

From: Mathieu Tortuyaux <[email protected]>

[ Upstream commit 89add40066f9ed9abe5f7f886fe5789ff7e0c50e ]

Tighten csum_start and csum_offset checks in virtio_net_hdr_to_skb for GSO packets.

The function already checks that a checksum requested with VIRTIO_NET_HDR_F_NEEDS_CSUM is in skb linear. But for GSO packets this might not hold for segs after segmentation.

Syzkaller demonstrated to reach this warning in skb_checksum_help

	offset = skb_checksum_start_offset(skb);
	ret = -EINVAL;
	if (WARN_ON_ONCE(offset >= skb_headlen(skb)))

By injecting a TSO packet:

WARNING: CPU: 1 PID: 3539 at net/core/dev.c:3284 skb_checksum_help+0x3d0/0x5b0
 ip_do_fragment+0x209/0x1b20 net/ipv4/ip_output.c:774
 ip_finish_output_gso net/ipv4/ip_output.c:279 [inline]
 __ip_finish_output+0x2bd/0x4b0 net/ipv4/ip_output.c:301
 iptunnel_xmit+0x50c/0x930 net/ipv4/ip_tunnel_core.c:82
 ip_tunnel_xmit+0x2296/0x2c70 net/ipv4/ip_tunnel.c:813
 __gre_xmit net/ipv4/ip_gre.c:469 [inline]
 ipgre_xmit+0x759/0xa60 net/ipv4/ip_gre.c:661
 __netdev_start_xmit include/linux/netdevice.h:4850 [inline]
 netdev_start_xmit include/linux/netdevice.h:4864 [inline]
 xmit_one net/core/dev.c:3595 [inline]
 dev_hard_start_xmit+0x261/0x8c0 net/core/dev.c:3611
 __dev_queue_xmit+0x1b97/0x3c90 net/core/dev.c:4261
 packet_snd net/packet/af_packet.c:3073 [inline]

The geometry of the bad input packet at tcp_gso_segment:

[   52.003050][ T8403] skb len=12202 headroom=244 headlen=12093 tailroom=0
[   52.003050][ T8403] mac=(168,24) mac_len=24 net=(192,52) trans=244
[   52.003050][ T8403] shinfo(txflags=0 nr_frags=1 gso(size=1552 type=3 segs=0))
[   52.003050][ T8403] csum(0x60000c7 start=199 offset=1536

ip_summed=3 complete_sw=0 valid=0 level=0)

Mitigate with stricter input validation.

csum_offset: for GSO packets, deduce the correct value from gso_type. This is already done for USO. Extend it to TSO. Let UFO be:
udp[46]_ufo_fragment ignores these fields and always computes the checksum in software.

csum_start: finding the real offset requires parsing to the transport header. Do not add a parser, use existing segmentation parsing. Thanks to SKB_GSO_DODGY, that also catches bad packets that are hw offloaded. Again test both TSO and USO. Do not test UFO for the above reason, and do not test UDP tunnel offload.

GSO packet are almost always CHECKSUM_PARTIAL. USO packets may be CHECKSUM_NONE since commit 10154db ("udp: Allow GSO transmit from devices with no checksum offload"), but then still these fields are initialized correctly in udp4_hwcsum/udp6_hwcsum_outgoing. So no need to test for ip_summed == CHECKSUM_PARTIAL first.

This revises an existing fix mentioned in the Fixes tag, which broke small packets with GSO offload, as detected by kselftests.

Link https://syzkaller.appspot.com/bug?extid=e1db31216c789f552871

Link https://lore.kernel.org/netdev/[email protected] open here

Fixes e269d79 ("net: missing check virtio")

Cc [email protected]

Signed-off-by Willem de Bruijn <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Jakub Kicinski <[email protected]>

Signed-off-by Mathieu Tortuyaux <[email protected]>

---
Hi,

This patch fixes network failures on OpenStack VMs running with Kernel 5.15.165.

In 5.15.165, the commit "net: missing check virtio" is breaking networks on VMs that uses virtio in some conditions.

I slightly adapted the patch to have it fitting this branch (5.15.y).

Once patched and compiled it has been successfully tested on Flatcar CI with Kernel 5.15.165.

NOTE: This patch has already been backported on other stable branches (like 6.6.y)

Thanks,

Mathieu - @tormath1

 include/linux/virtio_net.h | 17 ++++++-----------
 net/ipv4/tcp_offload.c     |  3 +++
 net/ipv4/udp_offload.c     |  4 ++++
 3 files changed, 13 insertions(+), 11 deletions(-)

include/linux/virtio_net.h +6 ~~-11~~

index 29b19d0a324c..d9410d97158d 100644
@@ -51,7 +51,6 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
 	unsigned int thlen = 0;
 	unsigned int p_off = 0;
 	unsigned int ip_proto;
-	u64 ret, remainder, gso_size;
 
 	if (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {
 		switch (hdr->gso_type & ~VIRTIO_NET_HDR_GSO_ECN) {

@@ -88,16 +87,6 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
 		u32 off = __virtio16_to_cpu(little_endian, hdr->csum_offset);
 		u32 needed = start + max_t(u32, thlen, off + sizeof(__sum16));
 
-		if (hdr->gso_size) {
-			gso_size = __virtio16_to_cpu(little_endian, hdr->gso_size);
-			ret = div64_u64_rem(skb->len, gso_size, &remainder);
-			if (!(ret && (hdr->gso_size > needed) &&
-						((remainder > needed) || (remainder == 0)))) {
-				return -EINVAL;
-			}
-			skb_shinfo(skb)->tx_flags |= SKBFL_SHARED_FRAG;
-		}
-
 		if (!pskb_may_pull(skb, needed))
 			return -EINVAL;

@@ -163,6 +152,12 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
 		if (gso_size == GSO_BY_FRAGS)
 			return -EINVAL;
 
+		if ((gso_size & SKB_GSO_TCPV4) ||
+			(gso_size & SKB_GSO_TCPV6)) {
+				if (skb->csum_offset != offsetof(struct tcphdr, check))
+					return -EINVAL;
+		}
+
 		/* Too small packets are not really GSO ones. */
 		if (skb->len - nh_off > gso_size) {
 			shinfo->gso_size = gso_size;

net/ipv4/tcp_offload.c +3 -0

index fc61cd3fea65..76684cbd63a4 100644
@@ -71,6 +71,9 @@ struct sk_buff *tcp_gso_segment(struct sk_buff *skb,
 	if (thlen < sizeof(*th))
 		goto out;
 
+    if (unlikely(skb_checksum_start(skb) != skb_transport_header(skb)))
+        goto out;
+
 	if (!pskb_may_pull(skb, thlen))
 		goto out;

net/ipv4/udp_offload.c +4 -0

index c61268849948..61773a26fb34 100644
@@ -279,6 +279,10 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
 	if (gso_skb->len <= sizeof(*uh) + mss)
 		return ERR_PTR(-EINVAL);
 
+    if (unlikely(skb_checksum_start(gso_skb) !=
+                skb_transport_header(gso_skb)))
+        return ERR_PTR(-EINVAL);
+
 	skb_pull(gso_skb, sizeof(*uh));
 
 	/* clear destructor to avoid skb_segment assigning it to tail */

Signature · 1 line

2.44.2

Greg KH

2024-09-05 07:41 UTC #1 lore raw

Quoted 81 lines · On Tue, Sep 03, 2024 at 10:42:26AM +0200, [email protected] wrote:

From: Mathieu Tortuyaux <[email protected]>
[ Upstream commit 89add40066f9ed9abe5f7f886fe5789ff7e0c50e ]
Tighten csum_start and csum_offset checks in virtio_net_hdr_to_skb for GSO packets.
The function already checks that a checksum requested with VIRTIO_NET_HDR_F_NEEDS_CSUM is in skb linear. But for GSO packets this might not hold for segs after segmentation.
Syzkaller demonstrated to reach this warning in skb_checksum_help
	offset = skb_checksum_start_offset(skb);
	ret = -EINVAL;
	if (WARN_ON_ONCE(offset >= skb_headlen(skb)))
By injecting a TSO packet:
WARNING: CPU: 1 PID: 3539 at net/core/dev.c:3284 skb_checksum_help+0x3d0/0x5b0
 ip_do_fragment+0x209/0x1b20 net/ipv4/ip_output.c:774
 ip_finish_output_gso net/ipv4/ip_output.c:279 [inline]
 __ip_finish_output+0x2bd/0x4b0 net/ipv4/ip_output.c:301
 iptunnel_xmit+0x50c/0x930 net/ipv4/ip_tunnel_core.c:82
 ip_tunnel_xmit+0x2296/0x2c70 net/ipv4/ip_tunnel.c:813
 __gre_xmit net/ipv4/ip_gre.c:469 [inline]
 ipgre_xmit+0x759/0xa60 net/ipv4/ip_gre.c:661
 __netdev_start_xmit include/linux/netdevice.h:4850 [inline]
 netdev_start_xmit include/linux/netdevice.h:4864 [inline]
 xmit_one net/core/dev.c:3595 [inline]
 dev_hard_start_xmit+0x261/0x8c0 net/core/dev.c:3611
 __dev_queue_xmit+0x1b97/0x3c90 net/core/dev.c:4261
 packet_snd net/packet/af_packet.c:3073 [inline]
The geometry of the bad input packet at tcp_gso_segment:
[   52.003050][ T8403] skb len=12202 headroom=244 headlen=12093 tailroom=0
[   52.003050][ T8403] mac=(168,24) mac_len=24 net=(192,52) trans=244
[   52.003050][ T8403] shinfo(txflags=0 nr_frags=1 gso(size=1552 type=3 segs=0))
[   52.003050][ T8403] csum(0x60000c7 start=199 offset=1536
ip_summed=3 complete_sw=0 valid=0 level=0)
Mitigate with stricter input validation.
csum_offset: for GSO packets, deduce the correct value from gso_type. This is already done for USO. Extend it to TSO. Let UFO be:
udp[46]_ufo_fragment ignores these fields and always computes the checksum in software.
csum_start: finding the real offset requires parsing to the transport header. Do not add a parser, use existing segmentation parsing. Thanks to SKB_GSO_DODGY, that also catches bad packets that are hw offloaded. Again test both TSO and USO. Do not test UFO for the above reason, and do not test UDP tunnel offload.
GSO packet are almost always CHECKSUM_PARTIAL. USO packets may be CHECKSUM_NONE since commit 10154db ("udp: Allow GSO transmit from devices with no checksum offload"), but then still these fields are initialized correctly in udp4_hwcsum/udp6_hwcsum_outgoing. So no need to test for ip_summed == CHECKSUM_PARTIAL first.
This revises an existing fix mentioned in the Fixes tag, which broke small packets with GSO offload, as detected by kselftests.
Link https://syzkaller.appspot.com/bug?extid=e1db31216c789f552871
Link https://lore.kernel.org/netdev/[email protected] open here
Fixes e269d79 ("net: missing check virtio")
Cc [email protected]
Signed-off-by Willem de Bruijn <[email protected]>
Link https://patch.msgid.link/[email protected] open here
Signed-off-by Jakub Kicinski <[email protected]>
Signed-off-by Mathieu Tortuyaux <[email protected]>
---
Hi,
This patch fixes network failures on OpenStack VMs running with Kernel 5.15.165.
In 5.15.165, the commit "net: missing check virtio" is breaking networks on VMs that uses virtio in some conditions.

Quoted 7 lines

I slightly adapted the patch to have it fitting this branch (5.15.y).
Once patched and compiled it has been successfully tested on Flatcar CI with Kernel 5.15.165.
NOTE: This patch has already been backported on other stable branches (like 6.6.y)

Now queued up, thanks.

gre gk-h

Greg KH

maintainer

2024-09-05 08:08 UTC #2 lore raw

In reply to [email protected]

Quoted 86 lines · On Tue, Sep 03, 2024 at 10:42:26AM +0200, [email protected] wrote:

From: Mathieu Tortuyaux <[email protected]>
[ Upstream commit 89add40066f9ed9abe5f7f886fe5789ff7e0c50e ]
Tighten csum_start and csum_offset checks in virtio_net_hdr_to_skb for GSO packets.
The function already checks that a checksum requested with VIRTIO_NET_HDR_F_NEEDS_CSUM is in skb linear. But for GSO packets this might not hold for segs after segmentation.
Syzkaller demonstrated to reach this warning in skb_checksum_help
	offset = skb_checksum_start_offset(skb);
	ret = -EINVAL;
	if (WARN_ON_ONCE(offset >= skb_headlen(skb)))
By injecting a TSO packet:
WARNING: CPU: 1 PID: 3539 at net/core/dev.c:3284 skb_checksum_help+0x3d0/0x5b0
 ip_do_fragment+0x209/0x1b20 net/ipv4/ip_output.c:774
 ip_finish_output_gso net/ipv4/ip_output.c:279 [inline]
 __ip_finish_output+0x2bd/0x4b0 net/ipv4/ip_output.c:301
 iptunnel_xmit+0x50c/0x930 net/ipv4/ip_tunnel_core.c:82
 ip_tunnel_xmit+0x2296/0x2c70 net/ipv4/ip_tunnel.c:813
 __gre_xmit net/ipv4/ip_gre.c:469 [inline]
 ipgre_xmit+0x759/0xa60 net/ipv4/ip_gre.c:661
 __netdev_start_xmit include/linux/netdevice.h:4850 [inline]
 netdev_start_xmit include/linux/netdevice.h:4864 [inline]
 xmit_one net/core/dev.c:3595 [inline]
 dev_hard_start_xmit+0x261/0x8c0 net/core/dev.c:3611
 __dev_queue_xmit+0x1b97/0x3c90 net/core/dev.c:4261
 packet_snd net/packet/af_packet.c:3073 [inline]
The geometry of the bad input packet at tcp_gso_segment:
[   52.003050][ T8403] skb len=12202 headroom=244 headlen=12093 tailroom=0
[   52.003050][ T8403] mac=(168,24) mac_len=24 net=(192,52) trans=244
[   52.003050][ T8403] shinfo(txflags=0 nr_frags=1 gso(size=1552 type=3 segs=0))
[   52.003050][ T8403] csum(0x60000c7 start=199 offset=1536
ip_summed=3 complete_sw=0 valid=0 level=0)
Mitigate with stricter input validation.
csum_offset: for GSO packets, deduce the correct value from gso_type. This is already done for USO. Extend it to TSO. Let UFO be:
udp[46]_ufo_fragment ignores these fields and always computes the checksum in software.
csum_start: finding the real offset requires parsing to the transport header. Do not add a parser, use existing segmentation parsing. Thanks to SKB_GSO_DODGY, that also catches bad packets that are hw offloaded. Again test both TSO and USO. Do not test UFO for the above reason, and do not test UDP tunnel offload.
GSO packet are almost always CHECKSUM_PARTIAL. USO packets may be CHECKSUM_NONE since commit 10154db ("udp: Allow GSO transmit from devices with no checksum offload"), but then still these fields are initialized correctly in udp4_hwcsum/udp6_hwcsum_outgoing. So no need to test for ip_summed == CHECKSUM_PARTIAL first.
This revises an existing fix mentioned in the Fixes tag, which broke small packets with GSO offload, as detected by kselftests.
Link https://syzkaller.appspot.com/bug?extid=e1db31216c789f552871
Link https://lore.kernel.org/netdev/[email protected] open here
Fixes e269d79 ("net: missing check virtio")
Cc [email protected]
Signed-off-by Willem de Bruijn <[email protected]>
Link https://patch.msgid.link/[email protected] open here
Signed-off-by Jakub Kicinski <[email protected]>
Signed-off-by Mathieu Tortuyaux <[email protected]>
---
Hi,
This patch fixes network failures on OpenStack VMs running with Kernel 5.15.165.
In 5.15.165, the commit "net: missing check virtio" is breaking networks on VMs that uses virtio in some conditions.
I slightly adapted the patch to have it fitting this branch (5.15.y).
Once patched and compiled it has been successfully tested on Flatcar CI with Kernel 5.15.165.

Quoted 6 lines

NOTE: This patch has already been backported on other stable branches (like 6.6.y)
Thanks,
Mathieu - @tormath1

How did you test this, it breaks the build for me:

net/ipv4/tcp_offload.c: In function ‘tcp_gso_segment’:
net/ipv4/tcp_offload.c:74:5: error: this ‘if’ clause does not guard... [-Werror=misleading-indentation]

   74 |     if (unlikely(skb_checksum_start(skb) != skb_transport_header(skb)))
      |     ^~
net/ipv4/tcp_offload.c:77:9: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the ‘if’
   77 |         if (!pskb_may_pull(skb, thlen))
      |         ^~
net/ipv4/udp_offload.c: In function ‘__udp_gso_segment’:
net/ipv4/udp_offload.c:282:5: error: this ‘if’ clause does not guard... [-Werror=misleading-indentation]
  282 |     if (unlikely(skb_checksum_start(gso_skb) !=
      |     ^~
net/ipv4/udp_offload.c:286:9: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the ‘if’
  286 |         skb_pull(gso_skb, sizeof(*uh));
      |         ^~~~~~~~

cc1: all warnings being treated as errors

Now dropped, please test your patches before sending them as it throws a big wrench in our process when things break...

thanks,

greg k-h